Phase modulation



'Mmmm Mi, E936, G. n.. USSIELMAN PHASE MODULATION 3 Sheets-Sheet l FiledApril 28, 1932 N M A M a Y S X E Rs N muy? R NL O H mm. Wm A .IO 4W. E/MW t G N www@ G. L, USSELMAN PHASE MODULATION Filed April 28, 1952 3Sheets-Sheet 2 INVENTOR GEORGE 1 USSELMAN w ATTOWNIEY /Q USS 3Sheets-Sheet 5 N Aw Mm mm Sm T, .E Lw .H GP.

Filed April 28, 1932 www FNVIENTOR GEORGE L. USSELMAN ATTORNEY PatentedMar. 31, 1936 UNITED STATES PATENT OFFICE PHASE MODULATION poration ofDelaware Application April 28, 1932, Serial No. 607,932

5 Claims.

The present invention relates to an improved method of and means forvarying the phase of radio waves or oscillations in accordance with thesignals to be transmitted.

In phase modulation transmitters as disclosed in United Statesapplication Serial Number 602,487 filed April 1, 1932, phase rotation ofthe wave relative to the normal wave is accomplished by the use ofinductance and capacity in the grid circuits of the modulator tubes. Ingeneral, transmitters of the type referred to above and known heretoforein the art, which use the inductance and capacity in the grid circuitsof the modulator tubes to cause phase rotation are satisfactory inoperation except where they are to be used with very short waves. Invery short wave signalling where ultrahigh frequency signallingoscillations are involved it is difficult to make coils and condenserswhich are easy to adjust. Especially is this true when a small amount ofphase modulation is required.

The primary object of the present invention is to provide a novel phasemodulation transmitter especially adapted to a shorter wave work.

Another object of this invention is to provide a novel phase modulationtransmitter especially applicable to shorter wave workin which a specialnovel means is provided by means of which the phase shift of the wavemay be easily and readily accomplished. In accordance with thisinvention the shift in phase may be accomplished in infinitely smallincrements or steps thereby making the present phase modulatedtransmitter especially applicable to shorter wave work.

Other objects of the present invention, and advantages to be gained bythe use thereof, will appear from the detailed description thereof whichfollows:

In its broadest aspect the transmitter of the present inventioncomprises two tubes of which the anodes are connected to a commonoscillating tank circuit, while the control electrodes are connected tothe same excitation source through separate lines so that one controlelectrode is excited through one line and the other control electrodeexcited through the other line. These two lines are of differentelectrical length. Biasing potential for the control electrodes of thetwo tubes is supplied from a common xed source. A signal frequencytransformer is arranged to vary the bias of the two control electrodesin phase opposition according to the signal modulations impressed on theprimary of the transformer. Since the two modulator tubes are excitedfrom the same source each is excited at (Cl. Z-17) the same frequency,but since each tube is excited over lines of different electricallengths the excitation of the tubes will be different in phase. Inaccordance with the present invention, one of these lines includes meansfor varying the elec- 5 trical length thereof in minute increments. Thiscomprises means similar to the trombone tuning means as disclosed inLindenblads United States Patent #1,821,386. Since the lines aredifferent in length, obviously, the phase of the energy supplied to onetube will be in advance of the phase of the energy supplied to the othertube. Likewise, due to the repeating effect of the tubes, the phase ofthe energy in the common tank circuit will be advanced or retarded fromthe aver- 15 age phase position of a normal radio wave and angle, thesign of which depends upon which modulator tube is supplying the greateramount 0f power. The tube having the lower instantaneous controlelectrode bias, which is the result 20 of the signal oscillationsdifferentially applied, as hereinbefore described, and the constantdirect current bias, will, of course, have a greater controlling effecton the phase of the oscillations in the tank circuit. In effect, thephase of the oscillations in the common tank circuit will be advanced orretarded from the average phase position of the oscillations in a mannersubstantially proportional to the anode current of one modulator tubeover the other. This difference of anode current of one modulator tubeover the other depends, of course, upon the eifective bias applied tothe control electrodes of the respective tubes. Since the signalfrequency transformer primary is energized by signal oscillations thecontrol electrode biasing excitation of the two phase modulator tubeswill vary at signal frequency and therefore the repeated energy in thecommon tank circuit will be varied in phase as the signal frequencyapplied to the transformer varies. 40

In modifications the modulation frequencies are applied to the screengrid electrodes of screen grid tubes from a source of signal frequenciesor by way of modulator tubes from a source of signal frequencies.

rIhe novel features of the invention have been pointed out withparticularity in the claims appended hereto.

The nature of the invention and the mode of operation thereof and thevarious advantages to be gained thereby will be understood from thefollowing description thereof and therefrom when read in connection withthe drawings attached hereto, throughout which like reference numeralsindicate like parts, and in which:

Figure 1 shows by way of illustration a phase modulation transmitter inwhich the novel features of the present invention are incorporated;while Figures 2 and 3 show modications of the arrangement of Figure 1.

Referring to the drawings, and in particular to Figure 1 thereof, Orepresents a master oscillator by means of which oscillations at thefrequency at which it is desired to signal are generated. Thisoscillator may be any type of oscillator known today and is preferablyan oscillator which produces oscillations of a constant frequency, forinstance, a long line controlled oscillator or a crystal controlledoscillator. The oscillator O supplies excitation to the controlelectrodes 2 and 4 of 'thermionic modulator tubes F and G over two pairsof lines L1 and L2. Lines L1 and L2 are connected to the oscillator Othrough blocking condensers 6 and 8. The line L1 is connected to thecontrol electrode 2 of tube F through blocking condenser 'I and by wayof blocking condenser 9 to ground 5 and from there to the cathode I oftube F. Line L2 is completed between the oscillator O and the controlelectrode 4 of modulator tube G by way of blocking condenser I I and tothe cathode I2 by way of blocking condenser I3, which is connected toground 5. In this manner potential oscillations at signal frequencyappearing in the lines L1 and L2 are impressed between the controlelectrodes and cathodes of tubes F and G, and normally theseoscillations would appear in like phase on the said control electrodes,The applicant has, however, provided as a part of the present inventiona novel means whereby the phase of the signal oscillations from O,reaching the control electrodes of tubes F and G respectively, areshifted a predetermined amount. This is accomplished in accordance` withthe present invention by making the line L2 of a constant predeterminedelectrical length, as indicated, and by providing in line L1 tuningmeans or means for adjusting the electrical length of the line L1 in theform of trombones T connected, as shown, and operated by means of acontrol element I4. Since these trombones per se form no part of thepresent invention a detailed description thereof is thought unnecessaryhere. However, it must be understood that in operation the trombones Tare slid up and down so that the amount of the elements I6 thereofexposed to the elements I8 thereof, determines to a certain extent theelectrical length of the line L1. It will be further understood that bythe use of these trombones to adjust the electrical length of the line,small changes in the electrical length of the line L1 can be made.Consequently, minute phase shifts between the energies reaching thecontrol electrodes of the tubes F and G may be made. Large changes inphase shift are to be accomplished by changing the relative lengths oflines L1 and L2. The high frequency oscillations impressed from Othrough lines L1 and L2 are repeated in the tubes F and G and appear onthe anodes 20 and 2| of tubes F and G respectively. These oscillationsare impressed in parallel on a common tank circuit 22 connected at oneterminal to anodes 20 and 2l and at the other terminal to a directcurrent potential source 23. Radio frequency oscillations are shuntedaround the source 23 by by-pass condensers C and C1. Since the highfrequency oscillations are applied co-phasally on the control electrodes2 and 4, the repeated oscillations appear co-phasally on the anodes 20and 2l and,

assuming the lines L1 and L2 are of equal length, they add in phase inthe tank circuit 22. However, since a certain desired phase shift hasbeen accomplished in the lines L1 and L2, the oscillations appear in 22in different phase depending upon the retardation applied thereto in L1.The tank circuit 22 is tuned to the normal frequency of the oscillationsgenerated in O by a variable capacity 24 and an inductance 25.

In order that the characteristic or nature of the energy in the tankcircuit 22 will be representative of signal oscillations impressedthereon, applicant has provided the following means. Direct currentbiasing potential is applied to the control electrode of tube F by wayof resistance R1 and to the control electrode of tube G by way ofresistance R2 from the source 23 by way of a lead 26 connected to thecenter point of the secondary winding 29 of a transformer T2, which willbe described more in detail hereinafter. The lower potential terminalsof resistances R1 and R2 are connected to the terminals of the secondarywinding 28 of modulation frequency transformer T2. The primary winding32 of trans former T2 is connected with a source of signal oscillations34.

Radio frequency oscillations appearing in the input circuit of tubes Fand G are shunted to cathodes Ill and I 2 respectively by way of by-passcondensers 28 and 30 respectively connected between the terminals ofbiasing resistance R1 and R2 respectively. This prevents said radiofrequency oscillations from being impressed on the transformer T2 andfrom there to the source of modulating frequencies. The condensers 28and 3Q also serve as blocking condensers with respect to the secondarywinding 2S of transformer T2, which will be described more in detailhereinafter. The impedance which the resistances R1 and R2 present atthe frequency of the oscillation generated in O must be equal to thesurge impedance of the lines L1 and L2 respectively so that there willbe no reflections taking place along the line and no constant Waves ofthe oscillator frequency built up therealong.

The operation of the transmitter described above and the manner in whichthe energy appearing in the tank circuit 22 is made to be characteristicof the signal oscillations will now be pointed out. In describing thisoperation it will be assumed that the oscillator O is generatingoscillations at the desired frequency and that the frequency of saidoscillations is constant. The control electrodes of tubes F and G willreceive excitation over the two pairs of lines L1 and L2. The line L2is, as disclosed above, of a predetermined fixed electrical length,while the line L1 may be varied as to electrical length to be shorter,equal to, or longer than the electrical length of line L2, as desired,by means of the trombones T. The difference in the electrical lines L1and L2 determines the amount of phase displacement between theexcitation delivered to the control electrode of tube F and the controlelectrode of tube G. This phase displacement or phase difference may bemade large or small by adjusting the electrical length of line L1 bymoving the trombones 'I in or out. The phase difference of theexcitation to the control electrodes of tubes F and G remains xed solong as the electrical lengths of lines L1 and L2 remain unchanged. Thephase of the oscillations in the common tank circuit 22 is controlled bythe power delivered from tubes F and G. The tank circuit 22 should beand is tuned to the frequency of the oscillator O. In normal operationthe phase of these oscillations will move about this frequency, that is,shift with respect to this frequency as an average. The power deliveredfrom each of the modulator tubes is controlled by the biasing potentialapplied to the control electrode thereof. Both tubes have, as describedhereinbefore, the same nxed biasing potential applied to their controlelectrode. In addition, however, the control electrode of each tube isexcited or energized in phase opposition by the secondary winding 29 oftransformer T2 so that when the modulating signals from source 34 areapplied to the primary winding of transformer T2 the biasing potentialof the control electrodes of tubes F and G will be varied in oppositedirections. This varies differentially the amount of energy delivered tothe tank circuit 22 by the tubes F and G. Since the phase of theexcitation of these tubes is different there is also a phase differencein the power delivered by the tubes to the tank circuit. The phase ofthe energy in tank circuit 22 therefore varies towards they phase of theenergy of that tube delivering the most power to the tank circuit andthis change will be substantially in proportion to the amount of currentdelivered by the said one modulator tube over that delivered by theother modulator tube.

The phase modulated energy appearing in the tank circuit 22 may beutilized in any manner. For example, it may be fed by way of aninductance lll coupled to the inductance 25 to an amplifier and/orfrequency multiplier 52, the output circuit of which is connected to anaerial system 4t. This unit i2 ampliiies and/or multiplies the phasemodulated energy and delivers it to the antenna.

While ordinarily there will be no appreciable amplitude modulationimparted to the oscillations developed at O, by means of this novelphase modulation system if any amplitude modulation is accomplished theenergy appearing in tank circuit 22 may be passed to the amplifierand/or frequency multiplier i2 by way of an amplitude limiting devicelll as shown by dotted lines in Figure l. This amplitude limiting devicewill correct any amplitude modulation which may take place.

In the modification shown in Figure 2 the radio frequency circuits andthe phase splitting means are in general similar to the correspondingelements of Figure l, and the operation in each case is in general thesame.

In the arrangement in Figure 2, however, modulation of the phase of theoscillations generated at signal frequency is accomplished in a somewhatdifferent manner. In Figure 2 the thermionic tubes F and G are of thescreen grid type, whereas the tubes F and G of Figure 1 are of the threeelectrode type. In Figure 2 direct current biasing potential only isapplied to the control electrodes 2 and l respectively by way of a leadi9 connected to a point on potentiometer P1 connected in parallel with aportion of the battery 23. The modulating frequencies are applied fromthe terminals of the secondary winding 29 of audio frequency transformerT1 over leads 5l) and 5l to the control electrodes 45 and M3 of tubes Fand G respectively. In the prior modification the source 34 wasconnected directly to the modulating circuit. In Figure 2, however, anaudio frequency amplifier 53 is interposed between the source 3d and theprimary winding 32 of the modulating transformer T1 so that the audiofrequency currents are amplified before they are impressed upon thescreen grid electrodes of tubes F and G. Charging potential for thescreen grid electrodes of the tubes F and G is supplied by way of a leadconnecting the electrical center of the secondary winding 2Q to a pointon potentiometer resistance P2 connected in parallel with a portion ofthe battery 23. The screen grids 45 and i6 are connected to ground byway of capacities 2l and it respectively. These capacities should belarge enough to have a low impedance for the oscillator frequency butthey should be small enough in capacity to have high impedance for thesignal frequency. The anodes 2i? and 2l of tubes F and G obtain theircharging potential from the source 23 by way of lead 52 connected to aterminal of the tank circuit 22. The phase modulated energy appearing intank circuit 22 is transferred by way of coupling capacity l0 to anamplifier and/or frequency multiplier 42 from which it is impressed onthe aerial system lli for radiation. Here, as in Figure 1, any amplitudemodulation may be taken care of my passing the phase modulated energythrough an amplitude limiter lli which may be interposed between thetank circuit 22 and the unit t2.

The operation of this arrangement is so similar to the operation of thearrangement disclosed in Figure l that a detailed description of theoperation thereof is thought unnecessary here. It will be noted,however, that only a normal negative biasing potential is applied to thecontrol electrodes 2 and d of tubes F and G. Audio frequencyoscillations applied to the screen grid electrodes 25 and 26 vary theinternal impedance and other characteristics including the amplificationfactor cf the tubes F and G respectively at audio frequency, therebyvarying the amount of energy applied by the respective tubes to the tankcircuit 22. As pointed out before, the energy in the tank circuit 22 isthe resultant of the combined energies supplied by tubes F and G. Thephase of the energy in the tank circuit 22 is determined by the phase ofthe energy from the tubes F or G which is supplying the greatest amountof energy at the particular instant to the tank circuit 22 because thisenergy will predominate and to a large extent determine the phase of theresultant energy in 22. In this manner phase modulation of the energy inthe tank circuit 22 is accomplished at signal frequency.

In the arrangement shown in Figure 3 the control electrodes of the tubesF and G respectively are excited only from the oscillator O and aremaintained at a constant direct current biasing potential frompotentiometer P1 by way of lead dil. The screen grid electrodes i5 and46 are excited by the signal frequency from the source 361 through theaudio frequency transformer T2 and the amplitude modulator tubes H and Iwhich have their control electrodes 52 and 53 connected to the oppositeterminals of the secondary winding 29, the electrical midpoint of whichis connected through a lead 25 to a point on potentiometer resistance P1to supply the biasing potential to the control electrodes 52 and 53. Theanode electrodes 56 and 5l of tubes H and I are connected in parallelwith the screen grid electrodes l5 and 46 of tubes F and G respectively.The charging potential for the screen grid electrodes i5 and i6 of tubesF and G respectively and the anode electrodes 56 and 5l of tubes I-I andI respectively is supplied from a potentiometer P2 connected in parallelwith battery 23 by Way of lead 60 and resistances Ra R4 respectively.Any change in the intensity of current flowing in the anode circuits oftubes H and I will obviously affect the potential applied to the screengrid electrodes 45 and 4G connected in parallel with said anode circuit.The filaments 54 and 55 of tubes H and I respectively are supplied withcurrent from the source 23 by connecting the same in parallel with thelaments I0 and l2 of tubes F and G respectively.

In operation it will be assumed that high frequency oscillations arebeing generated and applied to the control electrodes of tubes F and Gand appear in the tank circuit 22 thereof shifted in phase due to theeffect of the lines L1 and L2 on the high frequency oscillations. Whenthe control electrodes 52 and 53 of ,tubes H and I respectively aremodulated or varied at the signal frequency applied through thesecondary winding 29 the anodes 56 and 5l draw current in differentamounts depending upon the effective potential applied to the controlelectrodes. These varying currents in the anode circuits cause voltagedrops in R3 and R4 which are characteristic of the amplitude of themodulating frequencies. These voltage drops which are varying incharacteristic are applied to the screen grid electrodes 45 and 46 oftubes F and G. As pointed out in connection with the modification shownin Figure 2 the phase of the energy in the tank circuit is determined bythe phase of the energy repeated in the anode circuit of the tube whichis supplying the most energy to the tank circuit. In this manner phasemodulation of the energy in the tank circuit is accomplished at signalfrequency. The energy from the tank circuit 22 may be utilized in thesame manner in which the energy from the tank circuit 22 of Figure 2 isutilized.

I claim:

1. Means for modulating the phase of high frequency oscillations from asource comprising a pair of thermionic relay tubes each having an anode,a cathode, a control electrode and an auxiliary electrode, meansconnecting the anodes of said tubes in parallel with a tank circuit, aline of fixed length connecting said source of oscillations to thecontrol electrode and cathode of one of said tubes, a second lineconnecting said source of oscillations to the control electrode andcathode of the other of said tubes, tuning means having uniformdistributed capacity and inductance inserted in said last named line,and a circuit for applying oscillations which vary at signal frequencyin phase opposition to the auxiliary electrodes in each of said tubes.

2. In a signalling system, a pair of thermionic tubes, a load circuitconnected in parallel between the anodes and cathodes of said tubes,resistances connected between the control grid and cathode of saidtubes, means for applying modulating potentials in phase opposition tothe terminals of said resistances, high frequency conductors connectedbetween the control grids and between the cathodes of each of saidtubes, means in at least one of said conductors for Varying theelectrical length thereof, and means for applying high frequencyoscillations in displaced phase relation to said conductors.

3. In a signalling system, a pair of thermionic tubes each having ananode, a cathode, a control electrode and an auxiliary electrode, a Workcircuit connected in parallel with the anodes and cathodes of saidtubes, impedances connected between the control grids and cathodes ofsaid tubes, means for applying variable biasing potentials to similarpoints on said impedances, high frequency conducting lines connectedbetween the control grids of each of said tubes and between the cathodesof each of said tubes, variable reactances having distributed capacityand inductance in each of said conducting lines, m'eans for applyinghigh frequency oscillations to said lines, and a source of modulatingpotentials connected to the auxiliary electrodes of said tubes to applymodulating potentials in phase opposition to said electrodes.

4. In a signalling system, a pair of thermionic tubes of the screen gridtype, a work circuit connecting the anodes of each of said tubes to thecathodes of each of said tubes, means for applying biasing potentials tothe control grids of said tubes, high frequency conductors includingcapacitive and inductive reactances connected between the control gridsof each of said tubes and between the cathodes of each of said tubes,one of said reactances in each of said conductors being variable, meansfor applying high frequency oscillations displaced in phase to saidconductors, a pair of thermionic amplifiers, each having its anodeelectrode connected to the screen grid electrode in a different one ofsaid first named tubes, and means for applying modulating potentials inphase opposition to the control electrodes of said thermionicamplifiers.

5. A phase modulator comprising a pair of thermionic tubes each havingan anode, a control electrode, a cathode and an auxiliary electrode,m'eans for energizing the control electrodes of said tubes by phasedisplaced oscillations of like frequency, a tank circuit connected tothe anodes and cathodes of said tubes, said anodes and cathodes beingconnected in parallel, a source of modulating potentials, an impedance,a circuit connecting said source of modulating potentials to saidimpedance for impressing said modulating potentials on said impedance,and a circuit connecting points on said impedance at which saidmodulating potentials are of unlike phase to the auxiliary electrodes ofsaid tubes, thereby varying in unlike manner the conductivity of saidtubes in accordance with potential variations in said impedance.

GEORGE L. USSELMAN.

CII

